Sexual Development in Phytophthora

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This research will elucidate the developmental biology and genetics of mating and sexual spore development in oomycete fungi, using the plant pathogenic genus Phytophthora as a model. Oomycetes are an important but understudied group of lower eukaryotes that include many economically and environmentally significant pathogens of plants and animals, biocontrol agents of other pathogens, and saprophytes. In oomycetes as in many other microbes, mating is an important element of the life cycle. Mating results in the formation of oospores, which are durable structures that can survive season-to-season to initiate disease epidemics. The sexual cycle also enables gene flow through populations, yielding strains that may be more fit due to new combinations of loci determining pathogenicity, host preference, fungicide resistance, and other traits. Much of this proposal focuses on P. infestans, which is a devastating plant pathogen (potato late blight) that causes many billions of dollars of damage per year. It is also a good model system for studying oomycete biology. P. infestans is heterothallic, and oospores are normally induced when isolates of different mating types interact through hormones. In previous work, nine genes induced during mating were identified. In this project a multidisciplinary approach will be used to address the function and regulation of such mating-regulated genes. This will entail identifying additional regulated genes, and for a subset of the genes studying their structure, cellular localization of their protein products, and the effects of silencing and forced expression. In addition to studies of P. infestans, the expression of the genes will also be characterized in a homothallic species, P. phaseoli, which produces oospores in single culture. Preliminary studies of novel chemicals secreted during mating will also be performed. Results from this investigation will have conceptual as well as practical impacts. A better understanding will be obtained of the diverse strategies used to direct eukaryotic cell differentiation, to respond to stress, and to form survival structures. Important issues in development will be addressed such as cellular communication, self/nonself recognition, cell type determination, gene regulation, and signal transduction. The basis of homothallic and heterothallic mating systems will also be illuminated. It is likely that mating in oomycetes is regulated differently than in other lower eukaryotes such as ascomycetes and basidiomycetes, which lack taxonomic affinity to oomycetes. In the long term, if the factors which control mating can be identified, it might be possible to control plant diseases by manipulating the life cycles of pathogens using rational mechanism-based inhibitors instead of environmentally harmful chemicals.